Illumination apparatuses for automotive vehicles often use powerful incandescent light sources that generate an intense heat. These light sources are generally optically coupled to optical glass lenses since glass can withstand the generated heat and will not deform in use. However, the heat from most incandescent light sources is generally too high for optical lenses made of plastic materials.
Solid state light sources generate considerably less heat than incandescent light sources having the same illumination power. White LEDs are increasingly used as light sources in illumination apparatuses for the automotive industry, for example in head lights. Such illumination apparatuses can thus include optical lenses made of plastic materials because heat is not as high as with incandescent light sources.
Illumination apparatuses for automotive vehicles generally use thick lenses to project the light in front of the vehicles. The light beam from the light sources is projected as a magnified image and the lens refracts the light beams accordingly. Thick lenses have a high ratio between the thickness of the lens along the central optical axis and the thickness of the lens at the edges. These optical lenses are thus relatively thicker compare to optical lenses in other applications, as defined by the standard understanding in the industry in terms of the ratio between the key dimensions of optical lenses.
Thick lenses made of plastic materials are not easy to manufacture using usual injection molding methods because the injection molding process itself may cause deformations of the optical active surfaces. For instance, these lenses tend to shrink during cooling in a manner that reduces their accuracy and performances. Ultimately, the quality of thick lenses made of plastic materials can become an issue, particularly when high production volumes are required. One example of such context is the automotive and lighting industries. Using the known injection methods create challenges in terms of costs and complexities. Other injection molding issues can have a negative impact on the quality of thick lenses, particularly in terms of having a stable batch-to-batch consistency and surface accuracy.
Multistep injection methods for manufacturing plastic lenses have been used for several years. For instance, such method can include using rotary molds or shuttle molds to inject two or more layers of the same plastic material over one another with a clear boundary surface between each layer. However, several applications require stringent tolerances of the shape and the curvatures of optical lenses that can be difficult to obtain using these known methods, particularly for manufacturing thick lenses in large volumes.
Clearly, room for improvements always exists in this area of technology.